The Herpetic Eye Disease Study, Phase II, is a multi-institutional study of prevention of ocular herpes simplex infections. Two studies will be randomized comparisons of acyclovir vs. placebo for 1) prevention or delay of recurrences (HEDS-APT) and 2) prevention or delay of stromal keratitis or iritis subsequent to epithelial keratitis (HEDS-EKT). The third study (HEDS-RFS) is a nonexperimental study of potential triggers of recurrence of ocular herpetic disease. This application is to continue the current HEDS Coordinating Center (located at the Proctor Foundation, University of California, San Francisco) as the National Coordinating Center for HEDS Phase II. The National Coordinating Center's responsibilities will include data management, data quality control, statistical analyses, and administrative and technical support to HEDS committees, particularly the Data and Safety Monitoring, Steering, and Executive Committees.